Coaxial line section

ABSTRACT

A coaxial line section supported by a dielectric support of a high dielectric constant; an annular gap inside the support around the line section, which gap is filled with a material of low dielectric constant, like air.

waited States Patent Spinner 1 May 22, 1973 COAXIAL LINE SECTION 3,373,242 3/ 1968 Sewell ..174/28 X [76] Inventor: Georg Spinner, Erzgiessereistr. 33, 3391343 7/1968 Whitehead "174/ 28 Munich Germany 3,448,202 6/1969 Whitehead ..l74/28 3,573,342 3/1971 Graybill ..174/28 X [22] Filed: Aug. 6, 1971 211 App] 1 9 773 Primary Examiner-Bernard A. Gilheany Assistant ExaminerA. T. Grimley Attorney-Samuel Ostrolenk, Sidney G. Faber, [30] Foreign Application Priority Data Bernard Garb et 3].

Aug. 27, 1970 Germany ..P 20 42 565.6

[57] ABSTRACT [52} US. Cl. ..174/28, 174/15 C [51] Int. Cl. ..H0lb 9/04 A C axial lin section supported by a dielectric sup- [58] Field of Search ..174/28, 29, 36, 111, p rt f a hig dielectric constant; an annular gap in- 174/16 B, 99 B, 15 C side the support around the line section, which gap is filled with a material of low dielectric constant, like [56] References Cited air.

UNITED STATES PATENTS 11 Claims, 7 Drawing Figures 3,331,911 7/1967 Whitehead ..tl74/28 X PATENTEW- 3.735.016

SHEET 1 OF 2 Fig. 1

COAXIAL LINE SECTION The invention relates to a coaxial line section having a dielectric support whose inner cylindrical wall surface is disposed opposite a reduced-diameter wall portion of the inner conductor, leaving an annular gap. In a known arrangement of this type the annular air gap for suppressing glow discharge is provided in such a manner that the field strength within the annular air gap is less than 0.95 kV/mm. This avoids the danger of inadmissibly high field strengths arising within cavities which for production reasons are always present between the inner conductor portion and dielectric support unless galvanic coatings are applied to the support itself. Although the construction with a conductive coating avoids air inclusions and the occurrence of high field strengths it may happen that under a high current load the coating bursts and in addition the contacting at the end annular faces with the galvanic coating is extremely difficult.

In the aforementioned dielectric support arrangement the annular air gap was accordingly provided in order to handle relatively high field strengths at medium frequencies.

In contrast, the present invention is based on the solution of a problem which is related to the occurrence of high dielectric losses at higher frequencies and higher field strengths. In particular the invention relates to arrangements in which for mechanical reasons and because of the thermal stability dielectric support discs of a material having a high dielectric constant, for example ceramic material, must be used because for such applications supports of a material having a relatively low dielectric constant and low dielectric losses either do not have enough compressive strength (polytetrafluoroethylene) or have a thermal stability which is too low (polystyrene).

With such support discs of ceramic material or other material of high dielectric constant of about 4 to the dielectric losses arising at higher frequencies produce in known arrangements a heating which can lead to fracture of the support. The specific problem underlying the invention is therefore to reduce these dielectric losses and prevent fracture of the dielectric support due to heating.

According to the invention this problem is solved in that the width of the annular gap filled with a material of low dielectric constant is so chosen that the field strength is distributed between the dielectric of the annular gap and the dielectric of the disc in such a manner that the field strength within the support disc is not high enough to cause inadmissible heating. A particularly favorable arrangement is obtained if the annular gap is filled with air because the dielectric constant e l thereof is far smaller than that of the material of the disc (for example ceramic) and minimum losses arise.

In many cases it will not be possible to fill the annular gap with air over the entire axial length, for instance when the frictional engagement between the end annular faces of the inner conductor and the opposite annular faces of the dielectric support does not provide sufficient radial support. In this case the annular gap is completely or partially filled with supporting material of low dielectric constant and low dielectric losses. Such a material is for example polytetrafluoroethylene (PTFE). This may be introduced into the annular gap in the form of rings at both axial ends, in the form of a spiral or in the form of a cylindrical sleeve. Alternatively, radial support pins, for example of PTFE, may be inserted in radial bores of the inner conductor, said pins bearing in the assembled state on the inner wall of the ceramic disc.

Alternatively, a separate radial support may be provided adjacent the ceramic disc, the latter then only providing axial support. A separate radial support may for example be provided by way of an adjacent disc of PTFE which in the case of a gas-filled assembly can be the gas seal at the same time.

If the entire space of the annular gap is to be filled with air it is also possible to extend the dielectric support in its central portion axially on both sides and support it on the adjoining cylindrical portions of the inner conductor.

If a particularly high radial width of the annular gap is necessary then according to a further development of the invention the inner conductor is further reduced in diameter in the portion of the support disc and the resulting additional inductance compensated by annular beads which adjacent the dielectric support outwardly increase the diameter of the inner conductor.

Some examples of embodiment of the invention will be described hereinafter with the aid of the drawings, wherein:

FIG. 1 shows a dielectric support arrangement according to the invention,

FIG. 2 shows a dielectric support arrangement having supporting rings in the air gap,

FIG. 3 shows a dielectric support arrangement having a spiral in the annular gap,

FIG. 4 shows a dielectric support arrangement having a sleeve inserted in the annular gap,

FIG. 5 shows a dielectric support arrangement having supporting pins passing radially through the annular p FIG. 6 shows a dielectric support arrangement having a dielectric support supported radially on the extended portions of the inner conductor, and

FIG. 7 shows a further embodiment of the support arrangement according to the invention with compensation beads on the inner conductor adjacent the support.

In all the Figures the reference numeral 10 denotes the dielectric support which consists for example of ceramic material and the inner cylindrical wall surface 12 of which is radially spaced from the reduced-diameter portion 14 of the inner conductor 16 and together with said portion 14 defines an annular gap 18. This gap 18 is filled with air or a material which has a dielectric constant substantially smaller that that of the dielectric support 10 consisting for example of ceramic material and which exhibits substantially smaller dielectric losses.

The radial width of the annular gap 18 is so chosen that the field strength between the inner conductor and outer conductor is distributed amongst the dielectric support 10 and the annular gap 18 in such a manner that no field strengths which might cause excessive heating arise within the dielectric support 10.

In the example of embodiment according to FIG. 2 within the annular gap 18 there is provided at both radial ends a support ring 20 of PTFE or another material of low dielectric constant to provide radial support of the disc 10 on the portion 14.

In the example of embodiment according to FIG. 3 this radial support is provided by a spiral 22 of insulating material and in the embodiment according to FIG. 4 a sleeve 24 of insulating material is inserted. In the example of embodiment according to FIG. 5 radial support is provided by pins 26 which are inserted in radial bores of the inner conductor portion 14 and bear on the cylindrical wall surface 12. For example, three supporting pins may be provided at angular intervals of 120 at both axial ends.

According to the example of embodiment of FIG. 6 the annular gap 18 is filled with air and the dielectric support 10 is axially extended in the center portion towards both sides and is supported radially on the adjoining portions 28 of the inner conductor. With this example of embodiment further compensating measures are necessary with which the person skilled in the art is familiar and which are not shown in detail in the drawings. In the example of embodiment according to FIG. 7 for compensating the inductance resulting from the excessively deep recess 14 of the inner conductor the latter is provided with a compensation head 30 on both sides of the dielectric support 10. This bead 30 represents a capacitance and thus permits a deep recess in the inner conductor, enabling the width of the gap 18 to be made greater than in the embodiment of the inner conductor according to FIGS. 1 to 6.

If the annular gap 18 is to be filled only with air and the support inserts provided in FIGS. 2 to 5 are to be omitted and if in addition the frictional force between the end annular faces of the inner conductor 16 bearing on the dielectric support 10 is not sufficient to provide radial support, according to a further development of the invention an additional support disc 32 of a material of low e and low tg 8 may be used which as shown in dot-dash line in FIG. 1 is arranged adjacent a dielectric support 10, the latter then having to provide only the axial support. With compressed-gas-filled lines said insulating support 32 may also perform the function of a gas seal, which may be achieved in the examples of embodiment according to FIGS. 2 to 7 by means of additional resilient sealing like rings 33 in FIG. 2. In all the examples of embodiment the dielectric supports are compensated with respect to the characteristic impedance of the coaxial line.

I claim:

1. Coaxial line section having a dielectric support with an inner cylindrical wall surface that is disposed opposite a reduced-diameter wall portion of the inner conductor, thereby leaving an annular gap between said inner conductor wall portion and said inner cylindrical wall surface, characterized in that said annular gap is filled with a material of low dielectric constant and that the width of said annular gap is so chosen that the field strength is distributed between said dielectric material in said annular gap and said dielectric support in such a manner that within said dielectric support the field strength is not high enough to cause inadmissible heating.

2. Coaxial line section according to claim 1, characterized in that said annular gap is at least partially filled with a material which has a substantially smaller dielectric constant and substantially smaller dielectric losses than said dielectric support and said material being of a type which provides positive radial support between said inner conductor wall portion and said inner cylindrical wall surface.

3. Coaxial line section according to claim 2, wherein said gap has axial ends, characterized in that a ring of insulating material is inserted into said annular gap at each said axial end.

4. Coaxial line section according to claim 2, characterized in that a spiral of insulating material is inserted into said annular gap.

5. Coaxial line section according to claim 2, characterized in that said annular gap is filled with a sleeve of insulating material.

6. Coaxial line section according to claim 2, further including bores in and directed across said reduced diameter inner conductor portion characterized in that said dielectric support is supported radially by supporting pins of insulating material are inserted in said bores.

7. Coaxial line section according to claim 2, characterized in that said dielectric support is extended in the central region along the axial direction of said inner conductor, and at said extended central region it includes supports which are supported radially on adjacent portions of said inner conductor.

8. Coaxial line section according to claim 1, wherein said dielectric support has end faces, characterized in that said inner conductor is provided adjacent said end faces of said dielectric support with outwardly projecting beads.

9. Coaxial line section according to claim 1, characterized in that for radial support of said inner conductor, a separate insulating support also of .a materialof low dielectric losses is arranged adjacent said dielectric support.

10. Coaxial line section according to claim 9, characterized in that said separate insulating support simultaneously performs the function of a compressed-gas seal.

11. Coaxial line section according to claim 1, characterized in that to obtain a compressed-gas seal resilient sealing rings are provided. 

1. Coaxial line section having a dielectric support with an inner cylindrical wall surface that is disposed opposite a reduced-diameter wall portion of the inner conductor, thereby leaving an annular gap between said inner conductor wall portion and said inner cylindrical wall surface, characterized in that said annular gap is filled with a material of low dielectric constant and that the width of said annular gap is so chosen that the field strength is distributed between said dielectric material in said annular gap and said dielectric support in such a manner that within said dielectric support the field strength is not high enough to cause inadmissible heating.
 2. Coaxial line section according to claim 1, characterized in that said annular gap is at least partially filled with a material which has a substantially smaller dielectric constant and substantially smaller dielectric losses than said dielectric support and said material being of a type which provides positive radial support between said inner conductor wall portion and said inner cylindrical wall surface.
 3. Coaxial line section according to claim 2, wherein said gap has axial ends, characterized in that a ring of insulating material is inserted into said annular gap at each said axial end.
 4. Coaxial line section according to claim 2, characterized in that a spiral of insulating material is inserted into said annular gap.
 5. Coaxial line section according to claim 2, characterized in that said annular gap is filled with a sleeve of insulating material.
 6. Coaxial line section according to claim 2, further including bores in and directed across said reduced diameter inner conductor portion characterized in that said dielectric support is supported radially by supporting pins of insulating material are inserted in said bores.
 7. Coaxial line section according to claim 2, characterized in that said dielectric support is extended in the central region along the axial direction of said inner conductor, and at said extended central region it includes supports which are supported radially on adjacent portions of Said inner conductor.
 8. Coaxial line section according to claim 1, wherein said dielectric support has end faces, characterized in that said inner conductor is provided adjacent said end faces of said dielectric support with outwardly projecting beads.
 9. Coaxial line section according to claim 1, characterized in that for radial support of said inner conductor, a separate insulating support also of a material of low dielectric losses is arranged adjacent said dielectric support.
 10. Coaxial line section according to claim 9, characterized in that said separate insulating support simultaneously performs the function of a compressed-gas seal.
 11. Coaxial line section according to claim 1, characterized in that to obtain a compressed-gas seal resilient sealing rings are provided. 